2,860,951 United States Patent Office Patented Nov. 18, 1958

ee. sa has proven to be technologically or economically unat tractive. My invention comprises a combination of the first an 2,860,951 last of these approaches. Polyhalite deposits are found RECOVERY OF WALUES IN NATURALLY OCCUR 5 at depths ranging from 700 to 2000 feet and are often RNG ALKAL METAL SULFATE MENERALS interspersed with intrusions of halite (NaCl) and anhydrite George L. Cuzaningham, Cleveland Heights, Ohio, as (CaSO4). Polyhalite as mined in many instances con signor to Horizons incorporated tains as much as 13% sodium chloride, the removal of which is generally effected prior to any other treatment No Drawing. Application July 28, 1955 O of the ore in order to improve the recovery of potassium Seria No. 525,084 salts in the subsequent steps. The process variables to be considered in removal of the sodium chloride are dis 10 Claims. (CI. 23-32) cussed in detail in the aforesaid Bureau of Mines Bulletin. i have found that by rapid washing of the ore with This invention relates to a new and novel process for limited amounts of water at room temperature, over 95% the recovery of the alkali metal values in artificial or of the sodium chloride may be removed with an accom naturally occurring complex sulfates of alkali metals and panying loss of less than about 3% of the potassium sul one or more other metals, including calcium, magnesium, fate. Leaching with water at higher temperatures on the copper, manganese, lead, and aluminum. More particu order of 100° C. has been found to be unsuitable because larly it relates to a process in which the sulfate containing of the large amount of potassium sulfate lost in the ex material is sintered or fused with a proportioned amount traction liquid. . . . of acid oxide such as silica sand under conditions which After the sodium chloride has been removed by rapid insure the conversion of the other metal content of the washing, the polyhalite is heated with an acidic oxide, charge material from the sulfate to the silicate without preferably silica (SiO2) to a temperature between about any appreciable accompanying conversion of the alkali 500° C. and 1500° C. or even higher. As a result, the metal sulfate content of the charge material. alkaline earth Suifates are converted to alkaline earth Typical minerals which are amenable to the process silicates and sulfur dioxide is evolved from the heated constituting my invention include the following natural 2SS. ------or artificial ores: By varying the ratio of silica to polyhalite used in the 30 sintering or fusion operation, more or less of the alkaline earth content of the polyhalite is converted to the corre Name Formula sponding silicate. It is preferred to use an amount of Palmierite------(K,Na)2SO4.PbSO4 silica which is exactly stoichiometrically equal to the Vanthoffite----- 3Na2SO4.MgSO4 amount required to react with the alkaline earth sulfates, Glauberite--- -- Na2SO4.CaSO4 35 Langbeinite------K2SO4.2MgSO4 i. e. the calcium sulfate and magnesium sulfate, in the Manganolangbeinite K2SO4.2MnSO Syngenite.-- K2SO4·CaSO4.H2O polyhalite. When the amount of silica used is in excess Kroehnkite- Na2SO4.CuSO4.2H2O of the stoichiometric amount required to react with the Toewite--- Na2SO4.MgSO4.2%H2O Bloedite------Na2SO4.MgSO4.4H2O calcium sulfate and magnesium sulfate in the polyhalite, Wattevilleite--- n Na2SO4. CaSO4.4H2O then small amounts of potassium silicate may be formed Leonite------K2SO4.MgSO4.4H2O 40 by reaction with the excess. When the amount of silica Picromerite- K2SO4.MSO4.6H2O used is less than the amount required to react with both CyanochroitePolyhalite- K2SO4.2CaSO4.MgSO4.2H2OK2SO4.CuSO4.6H2O Leightonite- K2SO4.2CaSO4.CuSO4.2H2O the calcium sulfate and the magnesium sulfate, it has been Tamarugite- -- Na2SO4. Al2(SO4)3.12129 found that the silica preferentially reacts with the mag Mendozite---- - Na2SO4·Al2(SO4)3.22H2O Kalinite ------K2SO4·Al2(SO4)3.22H2O nesium sulfate, leaving some or all of the calcium sulfate Potassium Alum--- in the polyhalite unreacted...... Sodium Alum. Aiunite----- K2SO4.3Al2(SO4)3(OH)4 In order to obtain rapid reaction between the silica and Natroakunite Na2SO4.3Al2(SO4)3(OH)4 the polyhalite, I have found it advantageous to grind the Natrochalcit Na2SO4.3CuSO4.Cu(OH)2.2O sand and polyhalite prior to mixing the two ingredients. The reactants need not be dried since the presence of and others of even greater complexity. Because there are 50 small announts of water vapor has been found to be bene extensive deposits of polyhalite in the United States and ficial in the conversion of Stilfate to silicate. other parts of the world, and because the procedures are The silica used in the process need not be of high purity typical, this specification will describe the treatment of and ordinary sand as been found to be very suitable. polyhalite, it being usaderstood that tie techniques dis However, if the calcium silicate and magnesium silicate closed are equally applicable to the processing of many 55 are to be sold as white pigments or fillers, the sand used other naturally occurring ores or artificially groduced sui should be relatively low in iron and other impurities. . . fate containing minerals, such as hose listed above. Whatever the ratio of silica to polyhalite, the product Numerous efforts have been made to devise and to de of the sintering or fusion operation is next preferably velop processes for the recovery of potassium sulfate and leached with hot water. By extracting the residue from other salts from polyhalite, but until the present time the sintering operation with limited amounts of hot water no method has been successfully commercially exploited. it is possible to obtain solutions which are substantially The Bureau of Mines of the United States Department saturated with respect to potassium sulfate. Depending of the Interior has carried out extensive investigations on the recovery of various potassium salts from polyhalite on the ratio of silica to polyhalite, the extracts may also and has published a comprehensive report on the subject. contain unreacted alkaline earth sulfates or small amounts in Bulletin 459. Three general lines of investigation are of potassium silicate when excess silica is employed. discussed in the report as follows: (1) solution processes Although the potassium sulfate in the sintered mass employing no added chemicals other than water and pos has been found to be readily soluble in hot or cold water, sibly heat (2) reduction of the sulfates to sulfides or I have found that the extraction may be effected with oxides prior to solution processes and (3) decomposition minimal amounts of water by crushing the sintered prod by chemical reaction with various reagents such as lime, uct, or by quenching the fusion product directly in water carbon dioxide or ammonia. Each of these lines of attack and wet grinding the frit so produced. By extracting the 2,860,951 3 4 solid, crushed, ground or fritted residue with water at with respect to potassium sulphate which was recovered, 100 C. in counter current fashion, I have produced as previously described, by cooling the solution and per aqueous solutions containing approximately 24.1 grams mitting the potassium sulfate to crystalline out. The of potassium sulfate per 100 grams of water. On cool crystals were recovered by filtration, washed clean of ing the extract to 25 C., about one half of the potassium 5 mother liquor and then dried. The solid residue remain sulfate is precipitated as a crystalline product which is ing after repeated extractions with hot water was almost easily removed by filtration. The filtrate, or mother entirely pure calcium silicate, which when dried in use liquor, is reheated to 100° C. and employed to extract ful as a pigment, filler or soil conditioner. more potassium sulfate from the solid residue produced during the sintering or fusion step. The material remain O Example 3 ing after repeated washings is composed almost entirely The process of Example 2 was repeated except that of calcium silicate and magnesium silicate. Fresh water hot water was used to extract the magnesium sulfate from is employed to remove the last traces of potassium or the calcined polyhalite. The solid phase remaining was other soluble salts, the wash water being returned to potassium calcium pentasulfate (K2SO4.5CaSO4·H2O) the counter current extraction stage. The washed solid 5 instead of a mixture of syngenite and gypsum. The silicates are heated to remove water and when free of potassium calcium pentasulfate was . crushed and then moisture form a white powdered solid suitable as an intimately mixed with sufficient silica to convert the inert filler, or as a pigment, or as a corrective addition calcium sulfate to calcium silicate. The mixture was to acid soils. The following example of the process is sintered at about 900° C. for 30 minutes, after which the given by way of illustration and is not to be taken as 20 potassium sulfate was extracted with hot water. The limitative thereof. residue, calcium silicate, was dried and recovered as a Example I fine white, pigment grade powder. The potassium sul A mixture was formed comprising 22 parts by weight fate crystallized out of the extraction liquor when it was of silica which has been ground to -200 mesh (Tyler cooled to room temperature and was separated therefrom. Standard) and 65 parts of finely divided, -325 mesh 25 Example 4 (Tyler Standard) polyhalite. The polyhalite analyzed In still another variation of my process, polyhalite was 12.65% potassium, by weight; 4.8% magnesium, by rapidly leached free of halite and then calcined. The weight; 11.58% calcium, by weight; 60.96% sulfate, by calcine was extracted with a saturated solution of potas weight; and 2.92% sodium chloride. After the two mate 30 sium sulfate. The calcine and liquid were separated by rials were intimately mixed, the mixture was sintered at filtration. The filtrate was an aqueous solution of po temperatures between 880° C. and 950° C. for 70 tassium sulfate and magnesium sulfate which could be minutes. When cool, the sintered mass was ball milled readily separated by known techniques. The recovered with approximately 200 parts by weight of water. The potassium sulfate was saved for extraction of further resulting slurry was filtered and the precipitate was 35 amounts of calcined polyhalite. The solid cake ob washed with water. The filtrate and wash water con tained after filtration was almost entirely syngenite and tained 18.57 parts by weight of potassium sulfate which was heated with silica as in Example 2 to convert the represented 100% yield of potassium sulfate based on calcium sulfate to calcium silicate which was easily sep the polyhalite used. The wet cake was analyzed and arated from the potassium sulfate, by simple filtration. found to be a mixture of calcium and magnesium silicates. 40 In the above examples the potassium values in various The evolved gases from the sintering operation contained sulfate ores have been quantitatively recovered as sulfate. sulfur dioxide, which was not recovered. Where the For certain crops such as tobacco and citrus fruits, po operation is conducted on a large scale, the sulfur dioxide tassium sulfate is a preferred fertilizer constituent. For can be recovered by any suitable apparatus and con other uses, the potassium sulfate may be readily converted verted into sulfuric acid, sulfur, or other sulfur contain 45 to other potassium compounds by methods well known ing products by well known procedures. in the art. Instead of proceeding in the manner above described, While silica has been given by way of example, it is in which both the magnesium sulfate and the calcium to be understood that other acidic oxides such as titania, sulfate are converted to silicates, I have found that the ferric oxide, alumina, or zirconia may be employed to process may be varied in several ways without departing 50 convert the metal other than alkali metal content of the from the spirit or scope of my invention. complex sulfates to relatively insoluble titanates, ferrites, Where calcium silicate alone is desired, the process aluminates, zironates or the like. Accordingly the term may be conducted as follows: “acidic oxide' as employed in the following claims is to Example 2 be construed as including these and other oxides which 55 form relatively insoluble compounds with calcium, mag The polyhalite as mined was ground as before and nesium, copper, manganese and aluminum. washed rapidly with water to effect removal of most of Furthermore, although several treatments have been the sodium chloride. The washed polyhalite was cal specifically disclosed for a complex potassium sulfate, cined at about 450° C. and the calcine was treated with the process is equally applicable to complex sodium sul cold water (20° C.) to remove magnesium sulfate by 60 fates or complex mixed sodium-potassium sulfates, in dissolving same. The slurry produced was filtered to order to separate the alkali metal content from the other recover the magnesium sulfate in the filtrate, leaving a metal content. solid residue composed of syngenite (KSO.CaSOHO) I claim: and gypsum (CaSO4.2H2O). The solid residue was 1. A process for separating and recovering the alkali washed with an additional amount of water. The filtrate 65 metal sulfate content of a sulfate mineral consisting of at and wash water were combined and were evaporated to least one alkali metal sulfate from the group consisting of yield magnesium sulfate (MgSO4.7H2O) useful as Epsom sodium sulfate and potassium sulfate and at least one salts. The solid filter cake was ground and then mixed other sulfate from the group consisting of the sulfates of with sufficient finely divided silica to react with all of calcium, magnesium, aluminum, copper, lead and man the calcium sulfate present, The silica and the sulfate 70 ganese which comprises: freeing the sulfate mineral from containing material were intimately mixed and then were any chloride associated therewith by rapidly washing the heated to a temperature between 500° C. and 1500° C. sulfate mineral with cold water; forming an inti to convert the calcium sulfate to calcium silicate. The mate mixture of the washed sulfate mineral and sintered mass was extracted with a current of hot water. at least one solid oxide selected from the group The resulting aqueous solution was substantially saturated 75 consisting of silica, titania, zirconia, alumina, and iron 2,860,951 : 5 6 oxide, which oxides form relatively insoluble compounds potassium sulfate and at least one alkaline earth metal with the oxides of the metals of the second group enu sulfate which comprises: freeing the sulfate mineral from merated above; maintaining the mixture at a temperature any chloride associated therewith by rapidly washing between about 500° C. and 1500 C. for a time sufficient the sulfate mineral with cold water; forming an intimate to effect conversion of a substantial portion of the Sul mixture of the washed sulfate mineral and at least one fate mineral to the relatively insoluble compound of the solid oxide selected from the group of oxides consisting of added oxide; leaching the reaction mixture with Water silica, titania, zirconia, alumina, and iron oxide, all of at about 100° C. to extract the alkali metal sulfate from which form relatively insoluble compounds with the the insoluble reaction product; cooling the aqueous ex. oxides of the alkaline earths present in the mineral; main traction liquor sufficiently to crystallize the alkali metal O taining the mixture at a temperature between about 500 sulfate therefrom and recovering the said sulfate. C. and 150G C. for a time sufficient to effect conversion 2. A process for separating and recovering the alkali of at least some of the alkaline earth portion of the Sul metal sulfate content of a sulfate mineral consisting of fate mineral to the relatively insoluble compound of the at least one alkali metal sulfate and at least one other added oxide; leaching the reaction mixture with water at sulfate from the group consisting of the Sulfates of cal 15 about 100° C. to extract the potassium sulfate from the cium, magnesium, aluminum, copper, lead and manganese insolubie reaction product; cooling the aqueous extraction which comprises: freeing the sulfate mineral from any liquor sufficiently to crystallize the potassium sulfate and chloride associated therewith by rapidly Washing the recovering the said sulfate. sulfate mineral with cold water; forming an intimate mix. 6. A process for separating and recovering the alkali ture of the washed sulfate mineral and at least 9ne solid 20 metal sulfate content of a sulfate mineral consisting of at oxide selected from the group of oxides consisting of least one alkali metal sulfate from the group consisting silica, titania, zirconia, alumina and iron oxide, melting of sodium sulfate and potassium sulfate and at least one the mixture; maintaining the mixture in molten. form alkaline earth sulfate which comprises: freeing the sulfate for a time sufficient to effect conversion of a portion of mineral from any chloride associated therewith by rapid the sulfate mineral to a relatively insoluble compound 25 ly washing the sulfate mineral with cold water; forming of the added oxide; quenching the melt in an aqueous an intimate mixture of the washed sulfate mineral and medium; wet grinding the frit so produced; leaching the silica; maintaining the mixture at a temperature between ground frit with water at about 100° C. to extract the about 500 C. and 1500° C. for a time sufficient to effect alkali metal sulfate from the ground frit; cooling the conversion of at least some of the alkaline earth portion 30 of the Sulfate mineral to a relatively insoluble silicate; aqueous extraction liquor sufficiently to crystallize the leaching the reaction mixture with water at about 100° C. alkali metal sulfate therefrom and recovering the said to extract the alkali metal sulfate from the insoluble sulfate.3. A process for separating and recovering the alkali- silicate reaction product; cooling the aqueous extraction metal sulfate content of a sulfate mineral consisting of liquor sufficiently to crystallize the alkali metal sulfate at least one alkali metal sulfate and at least one other 35 therefrom and recovering the said sulfate. sulfate from the group consisting of the Sulfates of cal 7. A process for separating and recovering the potas cium, magnesium, aluminum, copper, lead and manga sium sulfate content of a polyhalite ore which comprises: nese which comprises: freeing the Sulfate mineral from freeing the ore from any chloride associated therewith by any chloride associated therewith by rapidly washing the rapidly washing the ore with cold water; forming an in sulfate mineral with cold water; forming an intimate 40 timate mixture of the washed ore and at least one solid mixture of the washed sulfate mineral and at least one oxide selected from the group of oxides consisting of solid oxide selected from the group of oxides consisting silica, titania, zirconia, alumina and iron oxide, which of silica, titania, zirconia, alumina and iron oxide, main form relatively insoluble compounds with the oxides of taining the mixture at a sintering temperature for a time the calcium and magnesium; maintaining the mixture at sufficient to effect conversion of a portion of the Sulfate 45 a temperature between about 500° C. and 1500° C. for a mineral to a relatively insoluble compound of the added time sufficient to effect conversion of at least the mag oxide; cooling the resulting sinter; leaching the cooled nesium sulfate portion of the polyhalite ore to the rela sinter with water at about 100° C. to extract the alkali tively insoluble compound of the added oxide; leaching metal sulfate from the insoluble reaction product; cooling the reaction mixture with water at about 100° C. to ex the aqueous extraction liquor sufficiently to crystallize the 50 tract the potassium sulfate from the insoluble reaction alkali metal sulfate therefrom and recovering the said product; cooling the aqueous extraction liquor sufficiently sulfate. to crystallize the potassium sulfate therefrom and re 4. A process for separating and recovering the alkali covering the said sulfate. metal sulfate content of a sulfate mineral consisting of 8. A process for separating and recovering the potas at least one alkali metal sulfate and at least one alkaline 55 sium sulfate content of a polyhalite ore which com earth metal sulfate which comprises: freeing the sulfate prises: freeing the polyhalite ore from any chloride asso mineral from any chloride associated therewith by rapidly ciated therewith by rapidly washing the ore with cold washing the sulfate mineral with cold water; forming an water; forming an intimate mixture of the washed poly intimate mixture of the washed sulfate mineral and at halite ore and at least one solid oxide selected from the least one solid oxide selected from the group of oxides 60 group of oxides consisting of silica, titania, zirconia, consisting of silica, titania, zirconia, alumina and iron alumina and iron oxide, which form relatively insoluble oxide, each of which forms relatively insoluble com compounds with the oxides of calcium and magnesium; pounds with the oxides of the alkaline earth metals maintaining the mixture at a temperature between about present in the sulfate mineral; maintaining the mixture 500 C. and 1500 C. for a time sufficient to effect con at a temperature between about 500 C. and 1500 C. for 65 version of at least some of the alkaline earth portion of a time sufficient to effect conversion of at least some of the polyhalite to the relatively insoluble compound of the alkaline earth sulfate portion of the sulfate mineral the added oxide; leaching the reaction mixture with water to the relatively insoluble compound of the added oxide; at about 100° C. to extract the potassium sulfate from the leaching the reaction mixture with water at about 100 C. insoluble reaction product; cooling the aqueous extraction to extract the alkali metal sulfate from the insoluble 70 liquor sufficiently to crystallize the potassium sulfate reaction product; cooling the aqueous extraction liquor therefrom and recovering the said sulfate. sufficiently to crystallize the alkali metal sulfate there 9. A process for separating and recovering the con from and recovering the said sulfate. stituents of a polyhalite ore which comprises: washing 5. A process for separating and recovering the potas the ore rapidly to remove the major portion of any sium sulfate content of a sulfate mineral consisting of 75 sodium chloride therein, calcining the washed polyhalite, 2,860,951 7 8 extracting the calcine with cold water to form a slurry, conversion of the alkaline earth sulfate to alkaline earth filtering the slurry to separate the slurry into a mag silicate, extracting the reaction product with water at nesium sulfate containing filtrate and a complex potas about 100° C., cooling the extraction liquor to precipi sium-alkaline earth sulfate solid residue, recovering the tate potassium sulfate and recovering the extracted solid magnesium sulfate from the filtrate by crystallization, residue consisting essentially of alkaline earth silicate forming an intimate mixture of the solid sulfate residue material. with silica, heating the mixture to a temperature be tween about 500° C. and 1500° C. to effect conversion References Cited in the file of this patent of the alkaline earth sulfate to alkaline earth silicate, ex UNITED STATES PATENTS tracting the reaction product with water at about 100 C., O cooling the extraction liquor to precipitate potassium sul 298.256 Townsend ------May 6, 1884 fate and recovering the extracted solid residue consisting 1,589,519 Dolbear ------June 22, 1926 essentially of alkaline earth silicate material. 1,794,551 Schoch ------Mar. 3, 1931 10. A process for separating and recovering the con 1,794,553 Schoch ------Mar. 3, 1931 stituents of a polyhalite ore which comprises: washing the ore rapidly to remove the major portion of any OTHER REFERENCES sodium chloride therein, calcining the washed polyhalite, Lange: "Handbook of Chemistry,' 8th edition, Hand extracting the calcine with water at about 100 C. to book Publishers, Inc., Sandusky, Ohio, 1952, pages 250 form a slurry, filtering the slurry to separate the slurry 251 and 276-277. into a magnesium sulfate containing filtrate and a com Storch: Industrial and Engineering Chemistry, vol. 22, plex potassium-alkaline earth sulfate solid residue, re No. 9, September 1930, pp. 934-941. covering the magnesium sulfate from the filtrate by crys Mellor: "Comprehensive Treatise on Inorganic and tallization, forming an intimate mixture of the solid sul Theoretical Chemistry,' Longmans, Green and Co., New fate residue with silica, heating the mixture to a tem . York, 1923, vol. 2, pp. 657 to 660. perature between about 500 C. and 1500 C. to effect